Combined method of area reduction

ABSTRACT

In the hydrostatic extrusion of a body through an opening, such as a die opening, the hydrostatic extrusion is begun by raising the pressure of the pressure fluid to a predetermined amount, and thereafter while continuing such pressure applying a tensile force to a portion of the body which is beyond the opening. The portion extending through the die may be preformed, or may be formed by the starting of hydrostatic extrusion. The end of the billet which engages the die is formed with double conicity.

United States Patent Nilsson July 24, 1973 1 COMBINED METHOD OF AREA 3,328,998 7/1967 Sabroff et al. 72/60 REDUCTION 3,455,134 7/1969 Thompson 3,6l8,35l l1/l97l Thompson [75] Inventor: Jan Nllssen, Robertsfors, Sweden 3,583,204 6/1971 Nilsson 72/60 [73] Assignee: Alimanna Svenska Elektriska Akti b h t vastel-as, Sweden Primary Examiner-Rwhard J. Herbst Attorney-Jennings Bailey, Jr. [22] F1led: Mar. 9, 1972 [21] Appl. No.: 233,151 [57] ABSTRACT In the hydrostatic extrusion of a body through an open- [30] Foreign Application Priority Data ing, such as a die opening, the hydrostatic extrusion is Mar. 18, 1971 Sweden 3486/71 begun y raising the Pressure of tha Pressure fluid to a predetermined amount, and thereafter while continu- 52 us. c1. 72/60, 721271 s such pressure pp y a tensile feree 10 a Portion 51 1m. (:1. B216 31/00 of the y which is beyond the p The portion 58 Field 61 Search 72/60, 271 extending through the die y be preformed, or y I be formed by the starting of hydrostatic extrusion. The [56] R f ren Cit d end of the billet which engages the die is formed with UNITED STATES PATENTS 2,558,035 6/1951 Bridgman 72/60 4 Claims, 4 Drawing Figures COMBINED METHOD OF AREA REDUCTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined method for reducing the area of a billet (solid or tubular) which is to pass through a die or drawing plate, the reduction being at least partially obtained by means of a combination of hydrostatic extrusion and drawing through the die or drawing plate.

2. The Prior Art Such combined methods are already known but have hitherto been found difficult to perform in practice. Endeavours have been made to use such a method for billets which are very difficult to deform when, for example, steel is being extruded which is found to need an extremely high extrusion pressure, but the means for providing such high pressure have not been available. Attempts have also been made to use combined methods for deforming tubes of more easily deformed material, for example, but as soon as a material more diffucult to deform is used problems become evident. It is impossible to start drawing immediately through a die or drawing plate, since without certain precautions cracks and damage would occur. For example if, when using steel, the drawing process where to be omitted or delayed too long, the strain would be too great on the high pressure equipment. A combined process has therefore only been discussed in theory for more easily processed materials or thin-walled tubes.

SUMMARY OF THE INVENTION The problems mentioned above are solved by means of the method according to the present invention which is characterised in that the drawing is initiated when the hydrostatic pressure has been increased to a certain level. The drawing thus only starts when the die has been surrounded on the upper side and the sides by a hydrostatic pressure which counteracts the stress caused when the drawing is started and protects the die from bursting. The billet may be shaped with a point for drawing or it may be provided with a point by means of hydrostatic extrusion in the first stage, for the application of drawing members, after which the combined area reduction can be initiated.

In a particularly prefrerred embodiment, the billet is shaped with a double-conical point, this providing a particularly suitable pressure/time curve for the deformation.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIG. 1 shows a combination of drawing and extrusion and FIG. 2 a diagram compressive force/time and tensile force/time for this deformation.

FIG. 3 shows a double-conical billet in a die and FIG. 4 shows the pressure/time diagram during deformation of this billet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a billet 11, which in this case is solid although the method can also be applied when prodcuing tubular products (around a stationary or movable mandrel, not shown). The billet is shaped with a protuberance 12. However, this protuberance can of course be produced by means of hydrostatic extrusion if the pressure available in the pressure chamber 13 is sufficient. The billet 11 may be of steel or some other material which is difficult to deform, or of compound material and it is ususally with the available pressure available in the chamber 13 to extrude the steel hydrostatically through the die 14 provided with a hole or the drawing plate.

It is therefore desirable in some way to facilitate the deformation of the billet 11 and a drawing member 15 is appled thereto at the point 12 of the billet (body). The deformation proceeds as follows:

FIG. 2 shows the combined process where first the pressrue P, in the pressure chamber is increased so much that the die is protected from bursting or other damage during the drawing initiated thereafter. The billet 11 is then drawn through the die 14 during continued hydrostatic extrusion (tensile force 32 P with the desired force up to a maximum (when the conical part of the billet has passed the die) after which the deformation work will be approximately constant.

The position of the billet 11 in relation to the die 14 is then determined when the extrusion and the drawing are to cease. This can be achieved, for example by means ofa limit breaker (not shown), which affects the pump for the pressure liquid 16, and also the drawing member 15. When a signal is obtained that the limit has been reached, the drawing member is first stopped (see FIG. 2) at P, and at the time (t t,), which in turn controls the pressure drop. However, it is normally impossible to prevent a brief pressure increase P before the pressure disappears in this type of pressure regulation.

In the case shown a constant compressive force (P is used during most of the process. It is also possible to allow the drawing member 15 to control the speed and the press is allowed to operate with constant pressure,

,for example by using a pressure limiter, not shown,

connected to the pressure cylinder 13. In this case the pressure increase P is not obtained.

FIG. 3 shows a billet 19 having a double-cone 17, 18. In this case it is not necessary to shape the billet 19 in advance, a protuberance 20 can be extruded hydrostatically in the initial stage. Due to the double-cone the pressure increase will occur in steps according to FIG. 4 as the conical parts pass. Extrusion is first performed to a point A (FIG. 4) when the point 20 starts to project from the die 21. When the first conical part has passed (at A),the pressure increase is checked becuase of the smaller cone angle of the part 18 and the pressure P increase to B. Drawing is then started (possibly after a temporary pause in the extrusion process) and the total pressure is then permitted to increase to C, where the conical part has passed the die, after which the pressure will remain constant, lying below the maximum pressure of the pressure-generating means P,,,.

The broken curve to D from A shows how the pressure P would be altered if drawing'assistance were not used before the entire point had been extruded. P would quickly be passed, resulting in damage or emergency stops.

A suitable extrusion pressure in the case shown may be 10 15 kbar, and suitable compressive force, up to a couple of hundred tons.

An apparatus for hydrostatic extrusion of a billet is shown in US Pat. No. 3,531,965.

The invention according to the above can be varied in many ways within the scope of the following claims.

I claim:

1. A method for reducing the area of a body which is to be passed through an opening of less cross section than that of the body, said method being a combination of hydrostatically extruding the body through the opening and applying a tensile force for pulling said body through said opening, which comprises starting the extrusion as hydrostatic extrusion only to extrude a minor part of the body through the opening, thereafter applying tensile means upon the extruded part of the body, thereafter increasing the extrusion pressure to a certain value and thereafter applying a tensile force to obtain maintaining the tensile force substantially constant. 

1. A method for reducing the area of a body which is to be passed through an opening of less cross-section than that of the body, said method being a combination of hydrostatically extruding the body through the opening and applying a tensile force for pulling said body through said opening, which comprises starting the extrusion as hYdrostatic extrusion only to extrude a minor part of the body through the opening, thereafter applying tensile means upon the extruded part of the body, thereafter increasing the extrusion pressure to a certain value and thereafter applying a tensile force to obtain a movement of the body through the opening with area reduction.
 2. A method as claimed in claim 1, in which the body has a double conical point at the front end.
 3. A method as claimed in claim 1, which comprises maintaining the hydrostatic extrusion pressure substantially constant after exertion of the tensile force begins and varying the tensile force to control the rate of extrusion.
 4. A method as claimed in claim 1, which comprises maintaining the tensile force substantially constant. 